The present invention relates to an elevating table for the transport of a disk-shaped workpiece to be moved up and down within an installation for the surface treatment of the workpiece, in particular within a vacuum installation with holding elements functioning for securing the workpiece on the elevating table as well as a method for transporting and securing a disk-shaped workpiece in a surface treatment chamber by means of an elevating table for the workpiece.
An elevating table of this type has the task of guiding a workpiece to be treated on its surface, to the treatment area in a working position. In vacuum installations this takes place within a separated chamber of the installation. During transport the workpiece must be secured on the elevating table so that it maintains a given position. In many cases a very particular position of the workpiece on the elevating table is required for the surface treatment process subsequently taking place. If these workpieces are for example semiconductor disks for the manufacture of integrated microelectronic chips, each disk as a rule has a contour deviating from the circular form wherein a circle segment is cut away which functions for the identification of the crystal orientation.
The disk support of the elevating table then has the same contour deviating from the circular form and the disk must with respect to this support be held and transported in this precisely oriented position.
It is known to use elastic gripper elements or holding elements for holding the workpiece tightly, which encompass the workpiece edge and which can be brought into different positions in order to hold the workpiece in one position.
It is known from EP-A-0 250 064 to provide elastic holding pistons on an elevating table, for the transport of a disk-shaped workpiece to be moved up and down within a vacuum installation for the surface treatment of the workpiece. The elastic holding pistons are provided at an incline to the workpiece surface or elevating table support surface which, at their projecting end, are provided with a protruding gripping head. These holding pistons are moved axially and clamp the workpiece tightly in a retracted position, onto the elevating table support.
For the surface etching of silicon wafers with different acids for example, it is further known from EP-A-0 316 296 to provide lifting cogs that are driven radially on the elevating table support and which encompass and tighten the workpiece to be treated.
Holding means of this type have the disadvantage that they are exposed to the surface treatment in essentially the same way as the workpiece. If it involves a coating then on these holding means or holding elements an increasingly thicker layer gradually forms. Thereby the ability of these means to function becomes questionable and due to their mechanical drive connection, replacement is very costly.
The like applies if the surface treatment is, for example, an etching process whereby the cited holding elements are gradually eroded which, in particular in vacuum processes, can impair the process by adding impurities.